"Asians are not all Chinese!"
Translation:아시아인은 다 중국인이 아니야!
While it is correct that "아시아인이 다 중국인은 아니야!" always translates to "Not all Asians are Chinese!", the exercise sentence could, though not always, also mean the same thing. This ambiguity comes from the fact that 다 can be both a noun and an adverb.
In your translation, 다 is used as a noun and the subject.
"Regarding Asians, all (of them) are not Chinese."
However, consider 아시아인은 as the subject as well as the topic, and 다 as an adverb.
"It is not (true) that all Asians are Chinese."
To make it clear, add 아직.
"아시아인은 아직 다 중국인이 아니야!"
This would probably always translate to "Not all Asians are Chinese yet."